Types of sampling
Cards (11)
- what is meant by the term 'sampling'?taking a small representative proportion of a habitat/population, then multiplying up number of individuals
- what problems can sampling cause?
- not always representative of population even if it's random
- could cause damage itself - trampling, digging pitfall traps
- what factors affect the number of samples to take?
- time availability
- diversity of habitat
- size of habitat
- what is a pilot study?
- where you record how many new species there are for each successive quadrat
- when this plateaus (e.g. don't find any new species) this represents the minimum number of quadrats to use
- why use random sampling?
- random to avoid bias in results
- ensures results are more representative of the habitat
- what is opportunistic sampling?
- weakest form of sampling as it may not be representative of population, uses organisms that are conveniently available
- what is stratified sampling?
- some populations can be divided into a number of strata (sub-groups) based on a particular characteristics
- a random sample is taken from each of these strata proportional to its size
- in which situations would systematic sampling be used?
- the effects of trampling if a footpath crosses a habitat
- the effects of light intensity as moving away from a tree
- a change in organisms along the bank of a river
- how do you complete a transect?
- rope/tape is stretched across a habitat
- in a large habitat
- record plants that touch the line at set intervals (e.g. every 2 meters)
- could also use quadrats at set intervals - called an interrupted belt transect, which produces quantitative data
- how do you complete a belt transect?
- place quadrat beside line
- move it along the line to sample a belt or band in greater detail
- produces quantitative data
- how can effects of unrepresentative data be minimised?
- use a larger sample
- greater number of individuals studies, the lower the probability that chance will influence the result